Intercommunicating telephone system.



L. D. BARROWS. INTERCOMMUNIGATING TELEPHONE SYSTEM.

APPLICATION TILED MAB..22,1912.

1,060,308, Patented Apr. 29, 1913.

Witnesses.

9 5 C In Ventor Leonll Barrows UNITED STATES PATENT 01 1 101 LEON D.BARROWS, OF NEW YORK, N. Y., ASSIGNOR TO AMERICAN TELEPHONE ANDTELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

INTERCOMMUNICATING TELEPHONE SYSTEM.

To all whom, it may concern:

Be it known hat I LEON D. Bannows, residing at New York, in the countyof New York and State of New York, have invented certain Improvements inIntercommunicating Telephone Systems, of which the following is aspecification.

This invention relates to intereommunieating telcihonc systems, andespecially to those which are connected through a trunk line to acentral station. It looks chiefly to the provision of such a system inwhich calls coming over a trunk may be readily transferred from one ofthe intercommunicating substations to another, without danger of eausina premature disconnect signal at the eentra station.

The accompanying drawing illustrates diagrammatically one ofthearrangements by which my invention may be efi'ectuated.

In the present instance but two stations, X and Y, of anintercommunicating system are shown, these being joined by a-trunk lineL, L to a central station (not shown). Each of the local stations hasthe usual tele- )llOIlO set S, talking current for which may suppliedfrom the common battery. over conductors L through suitable retardationcoils C; and is further provided with a contact apparatus K consistingof a series. of keys. Of the keys those designated as m and 7 at eachstation are for connecting the stations with each other, while keytserves to connect the local station with the trunk line, and key It isfor temporarily holding said trunk line, as will appear later. The keysmay be locked in a depressed position by a spring actuated plate, whichin moving to look any key releases that last depressed. in their lockedposition keys m and 1/, through opposite contacts 10 and 11 unite thetelephone set of the substation at which thcv are placed with pairs ofconductors I) and L multipled to similar contacts throughout the varioussubstations. An extra spring 12, when the keys (I: and 7/ are at thelimit of their depression below that in which they are locked, joins thebell of the telephone set of the corresponding station through a contactof the switch hook to conductors 18 and 14 14' leading to a localringing battery B. The key t at contacts 15 and 10, through conductorsL, bridges the telephone set of its station across the trunk, while athird contact 17 at the limit of the kcys downward movement connects theSpecification of Letters Patent,

Application flied March 22, 1912.

Patented Apr. 29, 1913.

Serial No. 685,441.

winding of a release relay R, common to all the'substatious of theintercommunicating system, to the battery ll by way of conductors 13 and18. The holding key- It eonnects, through contacts 10 and 20, thetelephone set of its substationnand conductors 18 and 21, the winding ofa holding relay R to battery ll. At its front contact 22 relay Rcontrols the introduction, in place of a substation set, of a bridgeacross the trunk for maintaining against operation the usual disconnectsignals at the central station. This bridge consists of a. conductor 23,containing the trunk line ringer O of the intcrcomniunicating system, acondenser 1 and a short circuit. 24 about the condenser closed by relaycontact 22. At its back contact 25 relay R, whcn'energized, opens ashort circuit QG-about a lockin and release relay R thewinding of whiciis included in .the trunk conductor L between the extremityof theholding bridge and the central station. {The front contact 27 of relay Rcloses a gap in av locking circuit 28 of holding relay R, through backcontact 10 of the release relay R and a front contact 29 of the holdingrelay, this locking circuit being independent of the original energizingcircuit through holdin kev h. It will be seen that the relays R and Rtogether furnish an electromagnetic apparatus upon the enerization ofwhich the maintenance of the iolding path depends.

hen a call comes into the intercommunicating system over the trunk line,we will assume that it is answered at substation X, and that asubscriber at substation Y is wanted. The subscriber at X pushes downthe key t, which looks and at contacts 15 and 16 bridges the telephoneset across the trunk, and talks with the calling party. Upon learningthat the call is for Y the holding key h is depress freeing the trunkkey If and current fin. ..rom battery B through the winding of relay It,conductor 21, contact 10 of key h, the telephone set of substation X(the receiver being off its hook), contact of key It and conductor 13 tobattery. Relay R operates, opening contact and the short circuit ofrelay R which is at once energized by current over the trunk. When thefront contacts 22 and 29 of relay R close. condenser P is shortcireuited through 'the former by conductor .24, making etiecti ve theholding bridge of the trunk through ringer O; and the contact 20 com'iletes thev locking circuit 28 for the holding relay, contact 19 of therelease relay R bein normally closed and contact 27 of relay T2 havingbeen made as described. The maintenance of the disconnect signal at thecentral station is now independent of the connection of the substationsets. The subscriber at station X next depresses the key y, releasingthe holding key h. In the extreme position of key y the closin ofcontact 12 rings the bell at substation from battery B through conductor14', hook switch of station conductors 31 and L, contacts 11 and 12 ofkev 3 and conductor 13. The subscriber at responding, locks down his key3 and upon removing the receiver from its hook is connected forconversation with the subscriber at X through contacts 10 and 11 of thetwo keys 1 and conductors L. Upon informing substation Y of the call,the subscriber at X may han up his receiver. The subscriber at Ydepresses the trunk key i and contacts 15, 16 bridgehis. telephone setacross the trunk. The momentary closing of contact 17 operates therelease relay R from batter B by way of conductors 13 and 18, and t isdrawing up its armature o Jens the locking circuit 28 of the holdingrelay R. The latter at contact 22 severs the direct current bridge ofthe trunk, and at contact 25 restores the 'short circuit of the windingof relay R deenergizing it. Said trunk is thus cleared for transmissionbetween-the callin and called subscribers. Since the rela governin thelocking circuit of the ho ding relay is in series with the trunk,it isunder the control of the central station operator, who,iftheintercommunicating subscribers fail to depress the trunkkeys-sutticiently to make'cont-act 17, and thus actuate the releaserelay R, can cut oil the central station battery by withdrawing thetrunk In and thus deeinergize relav R, opening die l ocking circuit ofthe holding relay at contact 27. Relay R may therefore be consideredboth as a locking and a secondary release relay.

Circumstances may arise which render my arrangement of the relay R withrelation to the other elements of the system of great advantage. Forexample an pose in a connection as enerally outiined above, the trunkkey at being locked down as a result of the previous use of theapparatus, that when the subscriber at Y answered he removed thereceiver from its hook beiore depressing the local answering key y. Thiswould cause the telephone set to be connected across the trun throu hthe contacts of key t, and were the relay in the holdmg bridge of thetrunk, would shunt it by a ow resistance path, causing its release. Thiswould unlock the holding relay opening the bridge 23, 24 and leaving thedisconnect signal at the central station dependent upon the connectionof the substation set. When the subscriber at Y continued the o )erationof answering the subscriber at X y actuating key 3 thus releasing key t,he would shift the telephone set from the trunk to the local circuit andthe disconnect signal would be actuated as a result of the completeremoval of the holding means, leading the central station operator towithdraw the trunk plug. But with the system arranged in accordance withmy invention, although such a procedure shunts the holding bridge,itdoes not det'energize the lockin and secondary release relay R This 5unit circuit may be traced from the juncture of the holding bridgecircuit with the trunk line L or one extremity of the holding bridge tocontact 15 of trunk key 5 b way of one of the conductors L, thence tlirough Ys telephone set to contact 16 of trunk key t, thence along thereturn conductor L, to the other extremity of the bridge where it joinstrunk line L. The current in the trunk is increased by the decrease ofresistance due to the connection of the low resistance loop, and thisflowing through the relay winding directly in the trunk insures againstrelease. A similar advanta e is gained by removing the release relay tfrom the trunk, where it is sometimes placed. For assumin the samesequence of acts on the )art 0 the subscriber at Y, the increase oicurrent due to the connection of the telephone set across the trunkthrough the contacts of key t, flowing through the windin of relay t nuseries with the trunk 'wouiii ener ize it, breaking the locking circuitof the iolding relay at. contact 10, and, as oefore, giving thedisconnect signal at the central station. I have so disposed the releaserelay that it it independent of variations in the trunk current and theholding means will be effective regardless of the manner in which thesubscriber responds.

I claim as my invention:

1. The combination with the local stations of an intercommunicatinsystem and their telephone sets, of a trunii line for connecting theinterconnnunicating system with a central station, means at each localstation for connecting its telephone set across the trunk, a ath forcurrent which may be substitute for the telephone set to hold the trunk,and electromagnetic apparatus upon the energization of which themaintenance of the holding path depends, said electromagnetic apparatushaving an energizing winding in the trunk line in the path of operatincurrents between the central statlon ant intercomuiunicating stations.

2. In a telephone system, a central stution, intercommunicating trunkconductors extending between the central station and interconnnunicatingstations, a telephone ill) lot]

ll i

set at the interconiiuunicatin Y stations and means for joining itstermina s to the trunk conductors, a trunk holding path connected at itsextremities to the trunk conductors and'which may be substituted for thetelephone set, and electromagnetic apparatus upon the energization ofwhich the maintenance of the holding pat-h depends, said electromagneticapparatus havin an energizing winding in a trunk eon uctor between theconnection of the holding path and the central station.

3. The combination with the local stations of an intercoinmunicatingsystem and their telephone sets, of a trunk line for connecting theintercommunicating system with a central station, means at each localstation for connecting its telephone set across the trunk, a at-h forcurrent which may be substituted or the telephone set to hold the trunk,and electromagnetic apparatus having independently energized windingsupon the encrgization of which the maintenance of the holdin pathdepends.

4. The combination with the local stations of an intercommunicatingsystem and their tele hone sets, of a trunk line for connecting 1 ieintercoininunicating system with a central station, means at each localstation for connectin its telephone set across the trunk, a )ath orcurrent which may be substituted or the telephone set to hold the trunk,and electromagnetic apparatus having independently ener ized windingsupon the energization of w ich the maintenance of the holding pathdepends, one of the windings being in series with the trunk line.

5. The combination with the local stations of an intercommunicatingsystem and their telephone sets, of a trunk line for connecting theintercommunicating system with a central station, key apparatus at eachlocal station for connecting its telephone set across the trunk, a pathfor current which may be substituted for thetelephone set to hold thetrunk, and relay apparatus havin a plurality of windings upon theenergization of each of which the holding path depends, the circuit ofone of which windings is overned by the key apparatus, the circuit 0another of the windings being in series with the trunk line.

6. The combination with the local stations of an intercommunicatinsystem, of a trunk line connected therewit a holding bridge for thetrunk line, means for closing the ridge and electromagnetic means foropening1 the bridge, said electromagnetic means aving an energizingwinding in series with the trunk line between the bridge and centralstation.

7. The combination with the local stations of an intcrcoinniunicaiingsystem, of a trunk line connected therewith, a holding bridge for thetrunk line, a holding relay for closing the bridge, anda relaycontrolled by the holding relay and serving when enerized to complete alocking circuit for said oldin relay.

8. Tie combination with the local stations of an intercoinniunicatingsystem, of a trunk line connected therewith, a holding bridge for thetrunk line, a holding relay for closing the bridge, and a locking relaycontrolled by the holding relay and serving when energized to complete alocking circuit for said holding relay, the locking relay beingenergized by current over the trunk line.

9. The combination with the local stations of an intercommunicatinsystem, of a trunk line connected therewit i, a holding bridge for thetrunk line, a holding relay for closing the bridge, and a locking relaycontrolled by the ho ding relay and serving when energized to connlete alocking circuit for said holdin re ay, the holding rclay beingenergizer. by local current and {he locking relay by current over thetlllllh inc. 10. The cgpnbination with the local stations of anintercoinniunicating system, of a trunk line connected therewith, aholdin; bridge for the trunk line, in its contacts the holding bridge,relay for the holding relay, and an energizin circuit for the releaserelay, said circuit being independent of the trunk line.

11. The combination with the stations of an intercommun catin system andtheir local battery, of a trun l r line connected with said stations, aholding bridge for the trunk line a relay controlling in its contactsthe. holding bridge, and a release rela for the holdin relay, saidrelease relay eing ena release ergize from the local battery.

12 The combination with the stations of an intercommunicatin system andtheir local battery, of a trun r line connected with a relaycoiitrolliii; 1

said stations, a holding bridge for the trunk line, a relay controllingin its contacts the holding bridge, and a plurality of release relaysfor the holding relay, one of said release rela 5 being energized fromthe local battery an another of said relays being energized over thetrunk line.

n testimony whereof, I have signed my name to this specification in thepresence 01' two subscribing witnesses, this sixteenth day of March,1912.

LEON D. BARROWS.

R. S. SU'HJFFE.

copies of this patent may be obtained for ave cent: each, by addressingthe "Ooinmintoner of ratenni. Washington, D. 0."

